U.S. patent application number 12/448674 was filed with the patent office on 2010-03-25 for pressure tank, in particular hydraulic accumulator.
Invention is credited to Herbert Baltes, Markus Lehnert.
Application Number | 20100071792 12/448674 |
Document ID | / |
Family ID | 39123749 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100071792 |
Kind Code |
A1 |
Baltes; Herbert ; et
al. |
March 25, 2010 |
PRESSURE TANK, IN PARTICULAR HYDRAULIC ACCUMULATOR
Abstract
In a pressure tank, in particular hydraulic accumulator (3, 5),
having a parting element (1), which parting element (1) separates a
space (11) for a first, in particular gaseous, working medium from
a space for a second working medium, in particular a fluid, in the
tank, is flexible, can move under deformation and defines a domed
main parting plane which extends from an annular edge (13), the
parting element (1) is produced from a substance which has a
fluoroplastic material, preferably a substance composed entirely of
fluoroplastic material.
Inventors: |
Baltes; Herbert; (Losheim,
DE) ; Lehnert; Markus; (Dillingen, DE) |
Correspondence
Address: |
ROYLANCE, ABRAMS, BERDO & GOODMAN, L.L.P.
1300 19TH STREET, N.W., SUITE 600
WASHINGTON,
DC
20036
US
|
Family ID: |
39123749 |
Appl. No.: |
12/448674 |
Filed: |
December 4, 2007 |
PCT Filed: |
December 4, 2007 |
PCT NO: |
PCT/EP2007/010500 |
371 Date: |
June 30, 2009 |
Current U.S.
Class: |
138/30 ;
92/103SD |
Current CPC
Class: |
F15B 1/10 20130101; F15B
2201/3153 20130101; F15B 2201/3155 20130101; F15B 2201/3151
20130101 |
Class at
Publication: |
138/30 ;
92/103.SD |
International
Class: |
F15B 1/10 20060101
F15B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2007 |
DE |
10 2007 003 724.6 |
Claims
1. A pressure tank, in particular a hydraulic accumulator (3, 5),
with a resilient separating element (1) which can be moved with
deformation and which separates a space (11) in the tank for a
first, in particular gaseous working medium, from a space for a
second working medium, in particular a fluid, and which defines a
domed main separating plane which extends from an annular edge
(13), characterized in that the separating element (1) is produced
from a substance which has a fluoroplastic material, preferably
consists entirely of fluoroplastic material.
2. The pressure tank according to claim 1, characterized in that
the separating element (1) defines a domed main separating plane on
whose side which lies inside relative to the dome annular bead-like
elevations (17, 19) are made projecting.
3. The pressure tank according to claim 2, characterized in that
succeeding elevations (17, 19) are separated from one another by
flat wall sections (23) which extend along the main separating
plane.
4. The pressure tank according to claim 2, characterized in that
the peaks of the annular bead-like elevations (17, 19) have a round
dome.
5. The pressure tank according to claim 2, characterized in that
the annular bead-like elevations are formed by folds (17, 19) which
are open on the outer side and form annular groove-like depressions
(27) in the main separating plane here.
6. The pressure tank according to claim 5, characterized in that
the height of at least one fold (17) measured from the open end to
the peak of the folds (17, 19) along its vertical axis (25) is
different relative to the height of other folds (19).
7. The pressure tank according to claim 6, characterized in that
the first fold (17) nearest the annular edge (13) has a smaller
height than the adjoining other folds (19).
8. The pressure tank according to claim 6, characterized in that
the height of the folds (17, 19) is larger at least by a factor of
two than the width of the annular groove-like depressions (27)
formed, which width is measured on the open end of the folds (17,
19).
9. The pressure tank according to claim 6, characterized in that
the vertical axes (25) of succeeding folds (17, 19) run tilted by a
small angle to one another.
10. The pressure tank according to claim 5, characterized in that
the flat wall sections (23) which extend between successive folds
(17, 19) each have the same wall thickness.
11. The pressure tank according to claim 9, characterized in that
the wall section which runs from the annular edge (13) to the
nearest first fold (17) has a wall thickness which on the annular
edge (13) has the largest value and decreases toward the first fold
(17) to the value of the wall thickness of the wall sections (23)
between the folds (17, 19).
Description
[0001] The invention relates to pressure tank, in particular to a
hydraulic accumulator, with a resilient separating element which
can be moved with deformation and which separates a space in the
tank for a first, in particular gaseous working medium, from a
space for a second working medium, in particular a fluid, and which
defines a domed main separating plane which extends from an annular
edge.
[0002] A pressure tank of this type in the form of a hydraulic
accumulator is disclosed in DE 28 52 912 A1. The resilient
separating element which consists of a rubber-like material
(synthetic rubber, such as acrylic nitrile-butadiene rubber), in
the known hydraulic accumulator forms a membrane which can be moved
by deformation and which separates the gas side from the liquid
side in the accumulator housing. Two main demands must be imposed
on the operating behavior of hydraulic accumulators with these
membranes which can be moved by deformation. On the one hand, the
impermeability of the membrane must be ensured to prevent gas
diffusion. On the other hand, corresponding mechanical properties
of the membrane are necessary, especially ease of movement and high
cyclic bending strength which are maintained even under the
influence of corrosive media.
[0003] In the aforementioned, known hydraulic accumulator these
requirements are only partially satisfied. In order to improve the
impermeability of the rubber-like membrane, in the known
accumulator there are annular bead-like elevations which project
out of the main separating plane in tight succession. Because the
elevations increase the average wall density, diffusion tightness
is in fact improved, but the significant increase of wall thickness
leads to considerable stiffening and accordingly to a deterioration
of mobility.
[0004] With respect to this prior art, the object of the invention
is to make available a pressure tank, in particular a hydraulic
accumulator, that is characterized by much improved operating
behavior in comparison.
[0005] According to the invention, this object is achieved by a
pressure tank which has the features of claim 1 in its
entirety.
[0006] In that, according to the invention, in the pressure tank
there is a separating element which is produced from a substance
which has a fluoroplastic material or consists preferably entirely
of fluoroplastic material, on the one hand outstanding diffusion
tightness is ensured, while on the other hand a separating element
is provided which has mechanical properties that are optimum for
use as a membrane in hydraulic accumulators, such as extreme cyclic
bending strength. Therefore, very small wall thicknesses can be
used; this leads to the desired ease of movement of the membrane.
Based on the resulting good response behavior, the pressure tank is
therefore especially well-suited for use as a pulsation damper.
[0007] Polytetrafluoroethylene has been found to be an especially
suitable material.
[0008] Polytetrafluoroethylene (PTFE) due to its very high melt
viscosity cannot be plastically molded, and the desired molded
article from this material is cold pressed from powdered raw
material with 200 to 400 bar and is sintered unpressurized at
370.degree. to 380.degree.. If films are to be obtained they are
generally peeled off solid cylindrical blocks.
Polytetrafluoroethylene therefore is commercially available in
general in the form of rigid solid bodies such as slabs, rods,
tubes, etc. For one with average skill in the art in the field of
membrane technology it is surprising that he can nevertheless
obtain separating elements which are produced in whole or in part
from polytetrafluoroethylene material and which have high mobility
such that they can even assume the function of a flexible rolling
membrane.
[0009] Since PTFE materials can moreover have especially good
chemical resistance, the pressure tank according to the invention
is also suitable for use in the presence of chemically corrosive
media.
[0010] In advantageous embodiments the separating element defines a
domed main separating plane on whose side, which lies inside
relative to the dome, annular bead-like elevations are made
projecting. By using a membrane which is domed in this way, in the
pressure tank a separating wall with a comparatively large area is
available which, with ease of deformation, can effect a
comparatively large change of volume of the bordering working
spaces in the pressure tank.
[0011] In preferred embodiments, succeeding elevations are
separated from one another by flat wall sections which extend along
the main separating plane. Therefore, between adjacent elevations
there is one free space at a time which is available for relative
movements of adjacent elevations so that without annular beads
which border one another mutually supporting one another and
stiffening the structure, the separating element can undergo
deformation as a rolling membrane.
[0012] Preferably, the peaks of the annular bead-like elevations
have a round dome so that notch effects are avoided.
[0013] In especially advantageous embodiments the annular bead-like
elevations are formed by folds which are open on the outer side and
form annular groove-like depressions in the main separating plane
here. According to the height of the folds, in a membrane which is
made in this way, similarly to the case of a bellows, an especially
great length of the material strip which can be moved is available
in order to roll up or pull out the membrane.
[0014] Preferably, the arrangement in this instance is made such
that the height of at least one fold measured from the open end to
the peak of the folds along its vertical axis is different relative
to the height of other folds.
[0015] As has been found, especially good mechanical properties are
obtained when the first fold nearest the annular edge has a smaller
height than the other adjoining folds.
[0016] In this respect, it is also advantageous if the wall section
which extends from the annular edge to the nearest first fold has a
wall thickness which on the annular edge has the largest value and
decreases toward the first fold to the value of the wall thickness
of the wall sections between the folds. The edge thickening formed
in this way, without adversely affecting the resilience of the
remaining membrane, promotes the clamping of the membrane on the
assigned housing element of the pressure tank and the formation of
a seal connection at the clamping site.
[0017] The invention is explained in detail below using the
drawings.
[0018] FIG. 1 shows a cutaway and slightly schematically simplified
longitudinal section of one exemplary embodiment of the pressure
tank according to the invention in the form of a hydraulic
accumulator, only the region of the bottom part of the housing and
the bordering part of the top part of the housing being shown;
[0019] FIG. 2 shows a longitudinal section of only the separating
element of the exemplary embodiment from FIG. 1, which element is
made as a rolling membrane, and which section is shown as one half
side and enlarged compared to FIG. 1, and
[0020] FIG. 3 shows a partial view of the region identified with
III in FIG. 2 which has been further enlarged compared to FIG.
2.
[0021] Of the exemplary embodiment of the pressure tank according
to the invention in the form of a hydraulic accumulator, FIG. 1
shows merely the bottom part 3 of the housing with a bottom-side
fluid connection 9 which is concentric to the longitudinal axis 7
of the housing, and a piece of the top part 5 of the housing which
borders the bottom part 3 of the housing. At the connection site
between the bottom part 3 of the housing and the top part 5 of the
housing the open, annular edge 13 of the separating element is
clamped tight in the form of a rolling membrane which is designated
as a whole as 1. Here the thickened edge 21 of the rolling membrane
1 on the one hand is supported on an annular surface 22 of the
bottom part 3 of the housing and on the other hand adjoins an
O-ring 15 which in turn sits in an annular groove 20 on an axially
projecting annular body 14 of the top part 5 of the housing.
[0022] FIGS. 1 and 2 show the roll membrane 1 in the completely
unrolled or extended state, in which the space 11 located above the
membrane 1 in FIG. 1, the gas side of the hydraulic accumulator has
the largest volume and there is no fluid pressure at the fluid
connection 9 so that the membrane 1 lies against the inside wall of
the bottom part 3 of the housing, a central reinforcing bead 29 of
the membrane 1 overlapping the edge of the fluid connection 9 and
in this way forming a mechanical safeguard against the membrane 1
being pressed into the fluid connection 9 when fluid pressure is
absent.
[0023] FIGS. 2 and 3 illustrate more details of the rolling
membrane 1 produced from PTFE material. Due to the very good
diffusion tightness of the PTFE material and especially good
strength properties, for the rolling membrane 1 merely a small wall
thickness of the membrane as is emerges from the annular edge 13 is
necessary; this defines the domed main separating plane. Successive
annular bead-like elevations project to the inside from this main
separating plane and are formed in the illustrated example, not by
beads in the form of solid bodies, but by folds, of which the first
fold nearest the edge 13 is designated as 17 and the adjoining
folds are each designated as 19. As is apparent from FIG. 1,
proceeding from the thickened wall 21 on the annular edge 13 the
wall thickness changes such that the wall thickness decreases as
far as the first fold 17 to the thickness value of flat wall
sections 23 which are each located between the folds 17 and 19. In
a practical embodiment the wall thickness decreases from the
thickening 21 to the first fold 18 from a value of 1.2 mm to a
value of 0.5 mm which is given on the succeeding wall section 23
between the folds 17 and 19. As FIG. 2 likewise shows, the
thickened edge 21 on the inside forms a type of shell shape which
forms a partial enclosure of the O-ring 15 which is not shown in
FIG. 2.
[0024] As can likewise be recognized from FIG. 2, the fold height
which is measured along the vertical axis 25 for the first fold 17
is smaller than for the succeeding folds 19 which each have the
same height, all folds 17 and 19 being domed at their peak. The
folds 17 and 19 are open on the side which is the outer side
relative to the dome, so that annular groove-like depressions 27
(see in particular FIG. 3) are formed which each form interruptions
in the course of the dome of the main separating plane between the
wall sections 23. As can be recognized especially from FIG. 3, the
inside width of the annular groove-like depressions 27 on the open
end of the folds 17, 19 is much smaller than the fold height
measured along the vertical axis 25, in this example the height of
the folds 19 being larger approximately by a factor of 4.
[0025] As is likewise apparent from FIG. 3, the insides of the
depressions 27 of the folds 17, 19 extend slightly diverging toward
the open end so that the open end of the depressions 27 has a
greater width than the base of the depressions 27 on the peak
region of the folds. As FIG. 2 shows, the vertical axes 25 of the
folds 19 each run in roughly the vertical direction to the
tangential plane to the adjacent wall sections 23, while the
vertical axis 25 of the first fold 17 extends slightly tilted to
this tangential plane, the vertical axis 25 of the first fold 17
enclosing an angle of approximately 10.degree. with the plane of
the annular edge 13. For the succeeding folds 19 the vertical axes
25 from fold to fold are tilted increasingly more steeply to the
plane of the edge 13.
[0026] In this example, the annular bead-like elevations projecting
on the inside of the membrane 1 are formed by folds 17 and 19, as a
result of which especially easy mobility for rolling up the
membrane results. But there could also be annular bead-shaped
elevations made as solid bodies. Unfilled PTFE materials can be
used, or those with a filler and/or filler combinations as can be
provided conventionally for PTFE materials; for example, when
extreme temperature resistance or other special properties are
desirable. Glass fiber materials, carbon, or metallic fillers can
be considered, among other materials.
[0027] Semifinished articles of PTFE materials are available in
many forms, for example, films peeled off blocks, solid bars, round
blanks, and the like. Based on the mechanical properties, finished
products, such as the rolling membrane used in the pressure tank
according to the invention, can be produced by cutting from molded
bodies; these bodies for their part are pressed and sintered from
powdered raw material. In particular, for thin-walled articles,
however, shaping by blow molding of a PTFE dispersion before
sintering is possible. If the spherical membrane shape shown in
FIG. 1 is obtained from a solid polytetrafluoroethylene body, it
can then be brought into the illustrated shape of the separating
membrane by cutting of the raw body. In order to minimize the
polytetrafluoroethylene scrap which forms in the cutting process,
preferably a preform body as the blank can be produced in a half
shell shape as a mold.
[0028] The indicated polytetrafluoroethylene material as a
fluoroplastic material can comprise both pure PTFE and also
modified PTFE and can include both unfilled PTFE and also PTFE
compounds. For a modified PTFE material, fillers such as bronze,
carbon dust, MoS.sub.2, as well as glass fiber and carbon fiber
materials are possible. In addition to PTFE, as other fluoroplastic
materials the following can be used: ethylene tetrafluoroethylene
(ETFE), ethylene chlorotrifluoroethylene copolymer (ECTFE),
polychlorotrifluoroethylene copolymer (PCTFE), perfluoroalkoxy
copolymer (PFA), polyvinylidene fluoride (PVDF) and
tetrafluoroethylene perfluoropropylene (FEP).
* * * * *